1. Technical Field
The present invention is related to toner, a development agent, and an image forming apparatus.
2. Background Art
Latent images formed electrically or magnetically are typically rendered visible by an electrophotographic image forming apparatus using toner (electrophotographic toner). For example, in electrophotography, electrostatic images (latent images) are formed on an image bearing member (typically a photoreceptor) and developed with toner to form visible toner images. The visible toner image is then transferred onto a transfer medium, typically paper, and thereafter fixed thereon. In the fixing process in which the toner image is fixed on the transfer medium, a thermal fixing device such as a heating roller fixing system or a heating belt fixing system is generally used for better energy efficiency.
In the current market, toner is demanded to have good low temperature fixability for energy saving.
To improve the low temperature fixability of toner, it is necessary to control the thermal characteristics of the binder resin accounting for a large ratio of the toner. In efforts to meet such an demand, for example, JP-2010-077419-A, JP-2012-083661-A, JP-2009-53695-A, and JP-2010-276754-A disclose regulating the composition and the thermal characteristics of a crystalline resin or toner having a good combination of low temperature fixability and high temperature stability of by providing a layer formed of particulates to the surface of the toner.
In addition, JP-2009-014926-A describes using a toner containing a binder resin formed of two kinds of crystalline resins (particularly preferably crystalline polyester resins) having different molecular weights under a particular fixing condition to improve the low temperature fixability of toner and prevent fixed images from cracking. In addition, JP-2010-151996-A discloses a toner containing a binder resin formed of two kinds of crystalline resins having different storage elastic moduli at 160° C. to have a good combination of low temperature fixability and high pressure stability.
However, in toner having a binder resin containing a crystalline resin, if the content of the crystalline resin accounts for a large ratio in the binder resin, the toner has an excellent low temperature fixability but with problems such that the toner is vulnerable to stirring stress in a development device, which easily leads to agglomeration of the toner and carrier over time, resulting in production of deficient images and in addition, it takes a time for re-crystallization of toner melted on a transfer medium during thermal fixing, meaning that the hardness of the surface of an image is not regained soon. These problems are ascribable to the properties of the crystalline resin. For this reason, marks of a member such as a discharging roller arranged in a discharging or transfer path are formed on the surface of an image after fixing, resulting in gloss change or damage thereof.
In attempts to solve these problems, for example, JP-3949526-B1 (JP-2004-038115-A) and JP-4513627-B1 (JP-2006-276305-A1) disclose a combinational use of a crystalline resin and a non-crystalline resin instead of using only a crystalline resin as the main component of a binder resin.
These are successful in compensating the defect about the hardness of the crystalline resin but are not satisfactory about improvement of the low temperature fixability thereby.